The only detailed biochemical and pharmacological studies that have been carried out on crystalline polypeptide toxins from marine sources are those from varieties of sea snakes. Because previous work has demonstrated that nematocysts of Physalia physalis (the Portugese man-o'-war) contain toxins which interfere with normal conduction of nervous impulses, which reduce blood pressure, which cause serum electrolyte changes, and which homolyze erythrocytes, we propose to isolate and chemically identify these toxins which are of polypeptide nature. To achieve these goals, we plan: (a) to isolate toxins from the nematocysts of Physalia physalis; (b) to monitor purification of these polypeptide toxins with a rapid, specific bioassay (to be defined); (c) to purify these compounds to homogeneity (by electrophoretic, chromatographic, and immunological criteria); (d) to determine molecular weight, chemical composition, amino acid sequence, and periodic structure of these toxins, bearing in mind the possibility that they may contain modified or unusual amino acids. Ultimately, when purified polypeptide toxins are obtained, their pharmacological actions on the nervous and cardiovascular systems should be examined in detail. It is hoped that the research proposed here will yield new therapeutic agents.